Scroll compressors are increasingly used to compress gasses in energy-efficient residential heat pumps and in refrigeration systems such as air conditioners. Uses of scroll compressors include their application in vacuum pumps, pumps for various gases, gas expanders, and engine blowers.
In such compressors, there is a stationary scroll member having an end plate and an involute or spiral wrap extending therefrom. A discharge port is typically defined within the end plate. Disposed in intermeshing relationship with the stationary scroll is an orbiting scroll, which also extends from an end plate. The orbiting scroll member is operatively connected to a driving shaft by a short-throw crank mechanism so that any given point on the orbiting scroll member describes an orbital trajectory in relation to a given point on the stationary scroll member.
The two scroll members are phased 180.degree. apart, i.e., one is a mirror image of the other. During relative motion between the stationary and orbiting scroll members, sealed pockets are formed between intermeshing involute scrolls, within which the gas to be compressed is confined. As orbital motion progresses, the sealed pockets undergo a reduction in volume. As a result, the sealed pockets act as compression chambers while the entrapped gas undergoes progressive confinement.
In such compressors, suction refrigerant gas enters the stationary and orbiting scroll members at their outer periphery. The meshing of the scrolls forms crescent-shaped pockets, which, starting from the periphery, reduce in size, thereby increasing the pressure of the trapped gas. The outermost pockets which are initially open to a suction chamber are sealed off as the orbiting scroll member touches the outside end of the fixed scroll member. The closed pockets move radially inward until they coalesce in communication with the discharge port, resulting in the expulsion of gas under high pressure.
The scroll compressor is unidirectional. It functions as a compressor when rotated in one direction, and as an expander when rotated in the opposite direction.
By controlling the number of wraps on the scroll members and the location of the discharge port, an optimum pressure ratio is established for a given compressor. Performance levels for such compressors also depend on the control of leakage.
As mentioned above, the pressure of refrigerant gas in the sealed pockets increases as their volume between the end plates is reduced by motion of the orbiting scroll in relation to the stationary scroll member. Entrance of the gas into a sealed pocket occurs through an intake passage before it is progressively compressed by a swirling motion of the scroll members. Entrapped gas is urged thereby toward the center of the scroll compressor. As the confined gas approaches the center, the sealed pockets converge further, while the gas is compressed even more. Proximate the center, the compressed gas escapes through the discharge port, from which it is guided into such external equipment as a condenser. From such external equipment, the compressed gas returns to an intake side of the compressor before the normal compression cycle is repeated.
Eccentric mounting of the orbital scroll member upon the driving shaft usually produces concomitant noise and vibration. In the past, problems of noise and vibration have been approached by multiplying the number of release ports. Illustrative of such approaches is Japanese patent application publication no. 2-5781 which bears a patent publication date of Jan. 10, 1990. That reference discloses the provision of multiple release ports at specified places on the stationary scroll member. Some loss of efficiency is incurred in such designs. Another approach, such as that disclosed in U.S. Pat. No. 4,626,179 which issued on Dec. 2, 1986 involves configuring the orbiting scroll member in relation to the fixed scroll member so that their respective lengths differ. As a result, gas pressure distribution within the fluid pockets is asymmetrical. This results in a larger moment of rotation for the orbiting scroll member, which is said to reduce vibration and noise. The disclosure of U.S. Pat. No. 4,626,179 is incorporated herein by reference.
The overall scroll wrap length is significant from a manufacturing viewpoint. Wrap length determines the manufacturing time required for machining each scroll wrap, which is one of the dominant cost (and productivity) factors.
In light of such problems, it would be desirable to reduce noise and vibration without increasing the number of release ports unnecessarily and without using different lengths of stationary and orbiting scrolls. Accordingly, the need has arisen to solve noise and vibration problems by delaying the initiation of compression in one sealed pocket in relation to another sealed pocket for reasons to be discussed below. The solution to such problems enables compressors to be produced which are more energy-efficient, lighter, and smaller than their predecessors.